Steady-state beam scanning and codebook generation

ABSTRACT

A method, an apparatus, and a computer-readable medium may be described in the present disclosure. The apparatus may be a user equipment. The apparatus may determine whether a number of unsuccessful repetitions associated with performance of a first type of scanning exceeds a repetition threshold. The apparatus may perform a second type of beam scanning based on the determination that the number of unsuccessful repetitions exceeded the repetition threshold.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of U.S. application Ser. No.15/684,861, entitled “STEADY-STATE BEAM SCANNING AND CODEBOOKGENERATION” and filed on Aug. 23, 2017, which claims the benefit of U.S.Provisional Application Ser. No. 62/426,110, entitled “STEADY-STATE BEAMSCANNING AND CODEBOOK GENERATION” and filed on Nov. 23, 2016. Thedisclosures of the aforementioned non-provisional and provisionalapplications are expressly incorporated by reference herein in theirentireties.

BACKGROUND Field

The present disclosure relates generally to communication systems, andmore particularly, to a user equipment configured to performsteady-state beam scanning and codebook generation.

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis 5G New Radio (NR). 5G NR is part of a continuous mobile broadbandevolution promulgated by Third Generation Partnership Project (3GPP) tomeet new requirements associated with latency, reliability, security,scalability (e.g., with Internet of Things (IoT)), and otherrequirements. Some aspects of 5G NR may be based on the 4G Long TermEvolution (LTE) standard. There exists a need for further improvementsin 5G NR technology. These improvements may also be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

Millimeter wave (mmW) systems may be deployed as part of variouswireless communications systems, such as 5G NR systems. Such mmW systemsmay provide relatively high data rates (e.g., relative to LTEcommunication) and/or provide relatively low latency (e.g., relative toLTE communication). In connection with mmW systems, beamforming may beutilized in order to achieve such relatively high data rates and/orrelatively low latencies.

One type of beamforming may include codebook-based beam scanning. Acodebook may include information corresponding to a beam used forcommunication, such as a beam index, direction, beam weights acrossantennas, antenna ordering information, beam steering information (e.g.,angles in azimuth and/or zenith), and/or other information associatedwith a beam. For example, a codebook may include a collection ofbeamforming vectors (e.g., fixed and/or predefined beamforming vectors),as well as techniques for generating and/or combining vectors (bothstatic as well as dynamic). Beamforming codebooks can be either designedfor rank-1 analog beamforming or for higher rank precoding applications.An example of a codebook may include a matrix of beam weights withdifferent column vectors corresponding to the weights used acrossdifferent antennas for a certain layer of data transmission.

In various aspects, use of a codebook blindly may increase latency. Thebeams in a codebook may be evaluated by a wireless device (e.g., a userequipment (UE)) based on channel measurements associated with beams,e.g., each time the UE generates or uses a beam. For example, a UE mayperform one or more measurements in order to determine beam indexesand/or directions (e.g., based on pilot or reference signals). Because awireless device may frequently perform measurements, latency may beincreased.

Various issues may affect the determination of the choice of beam(s)from the codebook. For example, paths and/or clusters may be blocked byobjects (e.g., other individuals, vehicles, buildings, or even the handor body of a user). Additionally, new paths/clusters may arrive ordisappear as objects move and channel conditions change. Further, beamsmay drift in time due to the movement of the wireless device, the user,and/or the blockers in the environment, which may affect paths and/orclusters.

With a steady-state approach for determining beams, a wireless devicemay determine a beam to use for communication based on informationassociated with beams (e.g., in a codebook). For example, a steady-stateapproach may include information associated with beams that areprioritized, e.g., so that the wireless device may select ahigh-priority beam pair for communication. Accordingly, the steady-stateapproach may allow a wireless device to select or determine a beam (orbeam pair) for communication more quickly than if the wireless devicewere to use a blind approach. In order to generate the beams (e.g.,based on a steady-state approach), a wireless device may need to performone or more measurements associated with one or more beams in order toidentify or determine a priority for beams (or beam pairs).

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided. In various aspects, the apparatus may bea wireless device, such as a UE. The apparatus may determine whether anumber of unsuccessful repetitions associated with performance of afirst type of beam scanning exceeds a repetition threshold. Theapparatus may perform a second type of beam scanning based on thedetermination that the number of unsuccessful repetitions exceeded therepetition threshold. In an aspect, the performance of the first type ofbeam scanning and the performance of the second type of beam scanningare based on a codebook. In an aspect, the apparatus may dynamicallyupdate the codebook based on current information associated with aserving beam. In an aspect, the number of unsuccessful repetitions hasnot exceeded the repetition threshold, and the apparatus may measure afirst value from the performance of the first type of beam scanning,wherein the first value is associated with a new serving beam, andswitch to the new serving beam based on a comparison of the first valueand a second value which is associated with a current serving beam. Inan aspect, the first value and the second value are based on asignal-to-noise ratio (SNR), a signal-to-interference-plus-noise-ratio(SINR), a signal-to-noise-plus-distortion ratio (SNDR), a receivedsignal strength indicator (RSSI), a reference signal received power(RSRP), or a beam reference signal received quality (B-RSRP), or anycombination thereof. In an aspect, the apparatus may determine toperform the first type of beam scanning before the second type of beamscanning. In an aspect, the determination to perform the first type ofbeam scanning before the second type of beam scanning is based on atimescale associated with the first type of beam scanning. In an aspect,the apparatus may determine the repetition threshold based on thetimescale. In an aspect, the timescale is determined based on at leastone of a mobility of the UE, an orientation of the UE relative to acluster arrival angle and a carrier frequency, output data from at leastone sensor associated with the UE, data from a cloud-based server, ordata from a base station. In an aspect, the data from the base stationor the data from the cloud-based server includes at least one of asequence of beams from which the UE determines beam coherence,information about an environment proximate to the UE, or a valueassociated with the timescale. In an aspect, the first type of beamscanning includes beam refinement using a first set of directional beamsassociated with a first subarray, the first subarray corresponding touse of a current serving beam, and wherein the second type of beamscanning includes beam scanning using a pseudo-omni beam associated witha second subarray that is different from the first subarray. In anaspect, the first type of beam scanning includes beam scanning using apseudo-omni beam associated with a second subarray that is differentfrom a first subarray, the first subarray corresponding to use of acurrent serving beam, and wherein the second type of beam scanningincludes beam refinement using a first set of directional beamsassociated with the first subarray.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating examples of a DLframe structure, DL channels within the DL frame structure, an UL framestructure, and UL channels within the UL frame structure, respectively.

FIG. 3 is a diagram illustrating an example of a base station and userequipment (UE) in an access network.

FIG. 4 is a diagram of a wireless communications system.

FIG. 5 is a flowchart of a method of wireless communication.

FIG. 6 is a flowchart of a method of wireless communication.

FIG. 7 is a flowchart of a method of wireless communication.

FIG. 8 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 9 is a diagram illustrating an example of a hardware implementationfor an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, and an Evolved Packet Core (EPC) 160. The basestations 102 may include macro cells (high power cellular base station)and/or small cells (low power cellular base station). The macro cellsinclude base stations. The small cells include femtocells, picocells,and microcells.

The base stations 102 (collectively referred to as Evolved UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access Network(E-UTRAN)) interface with the EPC 160 through backhaul links 132 (e.g.,S1 interface). In addition to other functions, the base stations 102 mayperform one or more of the following functions: transfer of user data,radio channel ciphering and deciphering, integrity protection, headercompression, mobility control functions (e.g., handover, dualconnectivity), inter-cell interference coordination, connection setupand release, load balancing, distribution for non-access stratum (NAS)messages, NAS node selection, synchronization, radio access network(RAN) sharing, multimedia broadcast multicast service (MBMS), subscriberand equipment trace, RAN information management (RIM), paging,positioning, and delivery of warning messages. The base stations 102 maycommunicate directly or indirectly (e.g., through the EPC 160) with eachother over backhaul links 134 (e.g., X2 interface). The backhaul links134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacro cells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (UL) (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (DL)(also referred to as forward link) transmissions from a base station 102to a UE 104. The communication links 120 may use multiple-input andmultiple-output (MIMO) antenna technology, including spatialmultiplexing, beamforming, and/or transmit diversity. The communicationlinks may be through one or more carriers. The base stations 102/UEs 104may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100 MHz) bandwidthper carrier allocated in a carrier aggregation of up to a total of YxMHz (x component carriers) used for transmission in each direction. Thecarriers may or may not be adjacent to each other. Allocation ofcarriers may be asymmetric with respect to DL and UL (e.g., more or lesscarriers may be allocated for DL than for UL). The component carriersmay include a primary component carrier and one or more secondarycomponent carriers. A primary component carrier may be referred to as aprimary cell (PCell) and a secondary component carrier may be referredto as a secondary cell (SCell).

Certain UEs 104 may communicate with each other using device-to-device(D2D) communication link 192. The D2D communication link 192 may use theDL/UL WWAN spectrum. The D2D communication link 192 may use one or moresidelink channels, such as a physical sidelink broadcast channel(PSBCH), a physical sidelink discovery channel (PSDCH), a physicalsidelink shared channel (PSSCH), and a physical sidelink control channel(PSCCH). D2D communication may be through a variety of wireless D2Dcommunications systems, such as for example, FlashLinQ, WiMedia,Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ NR and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing NR in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network.

The gNodeB (gNB) 180 may operate in millimeter wave (mmW) frequenciesand/or near mmW frequencies in communication with the UE 104. When thegNB 180 operates in mmW or near mmW frequencies, the gNB 180 may bereferred to as an mmW base station. Extremely high frequency (EHF) ispart of the RF in the electromagnetic spectrum. EHF has a range of 30GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters.Radio waves in the band may be referred to as a millimeter wave. NearmmW may extend down to a frequency of 3 GHz with a wavelength of 100millimeters. The super high frequency (SHF) band extends between 3 GHzand 30 GHz, also referred to as centimeter wave. Communications usingthe mmW/near mmW radio frequency band has extremely high path loss and ashort range. The mmW base station 180 may utilize beamforming 184 withthe UE 104 to compensate for the extremely high path loss and shortrange.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMEs 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService, and/or other IP services. The BM-SC 170 may provide functionsfor MBMS user service provisioning and delivery. The BM-SC 170 may serveas an entry point for content provider MBMS transmission, may be used toauthorize and initiate MBMS Bearer Services within a public land mobilenetwork (PLMN), and may be used to schedule MBMS transmissions. The MBMSGateway 168 may be used to distribute MBMS traffic to the base stations102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN)area broadcasting a particular service, and may be responsible forsession management (start/stop) and for collecting eMBMS relatedcharging information.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), or some other suitableterminology. The base station 102 provides an access point to the EPC160 for a UE 104. Examples of UEs 104 include a cellular phone, a smartphone, a session initiation protocol (SIP) phone, a laptop, a personaldigital assistant (PDA), a satellite radio, a global positioning system,a multimedia device, a video device, a digital audio player (e.g., MP3player), a camera, a game console, a tablet, a smart device, a wearabledevice, a vehicle, an electric meter, a gas pump, a toaster, or anyother similar functioning device. Some of the UEs 104 may be referred toas IoT devices (e.g., parking meter, gas pump, toaster, vehicles, etc.).The UE 104 may also be referred to as a station, a mobile station, asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal, a mobile terminal, a wireless terminal, a remoteterminal, a handset, a user agent, a mobile client, a client, or someother suitable terminology.

Referring again to FIG. 1, in certain aspects, the UE 104 may beconfigured to perform at least two types of beam scanning. A first typeof beam scanning may include beam refinement using a first set ofdirectional beams associated with a first subarray of the UE 104, andthe first subarray may correspond to use of a current serving beam. Inan aspect, this first type of beam scanning may be referred to asserving-subarray scanning. A second type of beam scanning may includebeam scanning using a pseudo-omni beam associated with a second subarrayof the UE 104. In an aspect, this second type of beam scanning may bereferred as alternate-subarray scanning.

In various aspects, the UE 104 may determine whether to perform a firsttype of beam scanning (e.g., serving-subarray scanning) before a secondtype of beam scanning (e.g., alternate-subarray scanning). That is, theUE 104 may prioritize a first type of beam scanning over a second typeof beam scanning. For example, the UE 104 may prioritizeserving-subarray scanning over alternate-subarray scanning, or viceversa (e.g., alternate-subarray scanning may be prioritized overserving-subarray beam scanning).

In one aspect, the UE 104 may determine to perform the first type ofbeam scanning over the second type of beam scanning based on a timescaleassociated with the first type of beam scanning. The timescale maycorrespond to a duration for which a current serving beam is expected toremain coherent (e.g., there is not radio link failure, channel qualitymeasurement(s) satisfy a threshold, etc.). For example, the timescalemay indicate a duration for which the current serving beam is estimatedto provide satisfactory communication with the base station 102.

According to various aspects, the UE 104 may determine the timescalebased on one or more of a mobility of the UE 104, an orientation of theUE 104 relative to a cluster arrival angle and/or a carrier frequency,output data from at least one sensor associated with the UE 104 (e.g.,an accelerometer, a gyroscope, etc.), data from the base station 102,and/or data from a cloud-based server. In one aspect, the UE 104 mayreceive, from the base station 102, a sequence of beams from which theUE 104 may determine beam coherence. The UE 104 may determine thetimescale based on the sequence of beams (e.g., based on tracking thebeams of the sequence). In another aspect, the UE 104 may receive (e.g.,from the base station 102 and/or a cloud-based server), a valueassociated with the timescale, such as a seed value from which the UE104 may determine the timescale.

In addition to the determination of the prioritization of beam scanning,the UE 104 may determine a repetition threshold. The repetitionthreshold may indicate a number of repetitions that the UE 104 is toperform the first type of beam scanning before performing the secondtype of beam scanning. In one aspect, the UE 104 may determine therepetition threshold based on a timescale. For example, a lower orshorter timescale (e.g., for a UE with a relatively high mobility), therepetition threshold may be correspondingly lower relative to a higheror longer timescale (e.g., for a UE with a relatively low mobility).

In order to find a better serving beam, the UE 104 may perform 198 thefirst type of beam scanning. The UE 104 may perform 198 the first typeof beam scanning based on a steady-state approach and, further, maydynamically update a codebook as the UE 104 performs 198 the first typeof beam scanning. If the UE 104 is able to find a better beam (e.g., abeam that offers more coherence than the current serving beam) whenperforming 198 the first type of beam scanning, the UE 104 may switch tothe new beam, which becomes the current serving beam.

In an effort to find a better beam, the UE 104 may repeatedly perform198 the first type of beam scanning until the repetition threshold isreached. If the UE 104 is unable to find a better beam than the currentserving beam based on performing 198 the first type of beam scanning,the UE 104 may then perform 198 the second type of beam scanning. Forexample, the UE 104 may perform 198 serving-subarray scanning until therepetition threshold is reached (e.g., four repetitions ofserving-subarray scanning) and, if the UE 104 is unable to find a betterbeam using the serving subarray, then the UE 104 may perform 198alternate-subarray scanning in order to determine if the UE 104 may usea better beam that corresponds to an alternate subarray. The UE 104 mayperform 198 the second type of beam scanning based on the codebook and,further, may dynamically update the codebook as the UE 104 performs 198the second type of beam scanning. In this way, the UE 104 may determinea current serving beam, which may offer satisfactory coherence and/ormay be estimated to remain coherent for a satisfactory duration.

FIG. 2A is a diagram 200 illustrating an example of a DL framestructure. FIG. 2B is a diagram 230 illustrating an example of channelswithin the DL frame structure. FIG. 2C is a diagram 250 illustrating anexample of an UL frame structure. FIG. 2D is a diagram 280 illustratingan example of channels within the UL frame structure. Other wirelesscommunication technologies may have a different frame structure and/ordifferent channels. A frame (10 ms) may be divided into 10 equally sizedsubframes. Each subframe may include two consecutive time slots. Aresource grid may be used to represent the two time slots, each timeslot including one or more time concurrent resource blocks (RBs) (alsoreferred to as physical RBs (PRBs)). The resource grid is divided intomultiple resource elements (REs). For a normal cyclic prefix, an RB maycontain 12 consecutive subcarriers in the frequency domain and 7consecutive symbols (for DL, OFDM symbols; for UL, SC-FDMA symbols) inthe time domain, for a total of 84 REs. For an extended cyclic prefix,an RB may contain 12 consecutive subcarriers in the frequency domain and6 consecutive symbols in the time domain, for a total of 72 REs. Thenumber of bits carried by each RE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry DL reference (pilot)signals (DL-RS) for channel estimation at the UE. The DL-RS may includecell-specific reference signals (CRS) (also sometimes called common RS),UE-specific reference signals (UE-RS), and channel state informationreference signals (CSI-RS). FIG. 2A illustrates CRS for antenna ports 0,1, 2, and 3 (indicated as R₀, R₁, R₂, and R₃, respectively), UE-RS forantenna port 5 (indicated as R₅), and CSI-RS for antenna port 15(indicated as R).

FIG. 2B illustrates an example of various channels within a DL subframeof a frame. The physical control format indicator channel (PCFICH) iswithin symbol 0 of slot 0, and carries a control format indicator (CFI)that indicates whether the physical downlink control channel (PDCCH)occupies 1, 2, or 3 symbols (FIG. 2B illustrates a PDCCH that occupies 3symbols). The PDCCH carries downlink control information (DCI) withinone or more control channel elements (CCEs), each CCE including nine REgroups (REGs), each REG including four consecutive REs in an OFDMsymbol. A UE may be configured with a UE-specific enhanced PDCCH(ePDCCH) that also carries DCI. The ePDCCH may have 2, 4, or 8 RB pairs(FIG. 2B shows two RB pairs, each subset including one RB pair). Thephysical hybrid automatic repeat request (ARQ) (HARQ) indicator channel(PHICH) is also within symbol 0 of slot 0 and carries the HARQ indicator(HI) that indicates HARQ acknowledgement (ACK)/negative ACK (NACK)feedback based on the physical uplink shared channel (PUSCH). Theprimary synchronization channel (PSCH) may be within symbol 6 of slot 0within subframes 0 and 5 of a frame. The PSCH carries a primarysynchronization signal (PSS) that is used by a UE 104 to determinesubframe/symbol timing and a physical layer identity. The secondarysynchronization channel (SSCH) may be within symbol 5 of slot 0 withinsubframes 0 and 5 of a frame. The SSCH carries a secondarysynchronization signal (SSS) that is used by a UE to determine aphysical layer cell identity group number and radio frame timing. Basedon the physical layer identity and the physical layer cell identitygroup number, the UE can determine a physical cell identifier (PCI).Based on the PCI, the UE can determine the locations of theaforementioned DL-RS. The physical broadcast channel (PBCH), whichcarries a master information block (MIB), may be logically grouped withthe PSCH and SSCH to form a synchronization signal (SS) block. The MIBprovides a number of RBs in the DL system bandwidth, a PHICHconfiguration, and a system frame number (SFN). The physical downlinkshared channel (PDSCH) carries user data, broadcast system informationnot transmitted through the PBCH such as system information blocks(SIBs), and paging messages.

As illustrated in FIG. 2C, some of the REs carry demodulation referencesignals (DM-RS) for channel estimation at the base station. The UE mayadditionally transmit sounding reference signals (SRS) in the lastsymbol of a subframe. The SRS may have a comb structure, and a UE maytransmit SRS on one of the combs. The SRS may be used by a base stationfor channel quality estimation to enable frequency-dependent schedulingon the UL.

FIG. 2D illustrates an example of various channels within an UL subframeof a frame. A physical random access channel (PRACH) may be within oneor more subframes within a frame based on the PRACH configuration. ThePRACH may include six consecutive RB pairs within a subframe. The PRACHallows the UE to perform initial system access and achieve ULsynchronization. A physical uplink control channel (PUCCH) may belocated on edges of the UL system bandwidth. The PUCCH carries uplinkcontrol information (UCI), such as scheduling requests, a channelquality indicator (CQI), a precoding matrix indicator (PMI), a rankindicator (RI), and HARQ ACK/NACK feedback. The PUSCH carries data, andmay additionally be used to carry a buffer status report (BSR), a powerheadroom report (PHR), and/or UCI.

FIG. 3 is a block diagram of a base station 310 in communication with aUE 350 in an access network. In the DL, IP packets from the EPC 160 maybe provided to a controller/processor 375. The controller/processor 375implements layer 3 and layer 2 functionality. Layer 3 includes a radioresource control (RRC) layer, and layer 2 includes a packet dataconvergence protocol (PDCP) layer, a radio link control (RLC) layer, anda medium access control (MAC) layer. The controller/processor 375provides RRC layer functionality associated with broadcasting of systeminformation (e.g., MIB, SIBs), RRC connection control (e.g., RRCconnection paging, RRC connection establishment, RRC connectionmodification, and RRC connection release), inter radio access technology(RAT) mobility, and measurement configuration for UE measurementreporting; PDCP layer functionality associated with headercompression/decompression, security (ciphering, deciphering, integrityprotection, integrity verification), and handover support functions; RLClayer functionality associated with the transfer of upper layer packetdata units (PDUs), error correction through ARQ, concatenation,segmentation, and reassembly of RLC service data units (SDUs),re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto transport blocks(TBs), demultiplexing of MAC SDUs from TBs, scheduling informationreporting, error correction through HARQ, priority handling, and logicalchannel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 316 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 374 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 350. Each spatial stream may then be provided to a differentantenna 320 via a separate transmitter 318TX. Each transmitter 318TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 350, each receiver 354RX receives a signal through itsrespective antenna 352. Each receiver 354RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 356. The TX processor 368 and the RX processor 356implement layer 1 functionality associated with various signalprocessing functions. The RX processor 356 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 350. If multiple spatial streams are destined for the UE 350,they may be combined by the RX processor 356 into a single OFDM symbolstream. The RX processor 356 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe base station 310. These soft decisions may be based on channelestimates computed by the channel estimator 358. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the base station 310 on the physicalchannel. The data and control signals are then provided to thecontroller/processor 359, which implements layer 3 and layer 2functionality.

The controller/processor 359 can be associated with a memory 360 thatstores program codes and data. The memory 360 may be referred to as acomputer-readable medium. In the UL, the controller/processor 359provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing to recover IP packets from the EPC 160. Thecontroller/processor 359 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the base station 310, the controller/processor 359provides RRC layer functionality associated with system information(e.g., MIB, SIBs) acquisition, RRC connections, and measurementreporting; PDCP layer functionality associated with headercompression/decompression, and security (ciphering, deciphering,integrity protection, integrity verification); RLC layer functionalityassociated with the transfer of upper layer PDUs, error correctionthrough ARQ, concatenation, segmentation, and reassembly of RLC SDUs,re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto TBs,demultiplexing of MAC SDUs from TBs, scheduling information reporting,error correction through HARQ, priority handling, and logical channelprioritization.

Channel estimates derived by a channel estimator 358 from a referencesignal or feedback transmitted by the base station 310 may be used bythe TX processor 368 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 368 may be provided to different antenna352 via separate transmitters 354TX. Each transmitter 354TX may modulatean RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the base station 310 in a mannersimilar to that described in connection with the receiver function atthe UE 350. Each receiver 318RX receives a signal through its respectiveantenna 320. Each receiver 318RX recovers information modulated onto anRF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 thatstores program codes and data. The memory 376 may be referred to as acomputer-readable medium. In the UL, the controller/processor 375provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 350. IP packets from thecontroller/processor 375 may be provided to the EPC 160. Thecontroller/processor 375 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

FIG. 4 is a diagram of a wireless communications system 400. Thewireless communications system 400 may include a base station 402 and aUE 404. Extremely high frequency (EHF) is part of the RF in theelectromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and awavelength between 1 millimeter and 10 millimeters. Radio waves in theband may be referred to as a millimeter wave (mmW). Near mmW may extenddown to a frequency of 3 GHz with a wavelength of 100 millimeters (thesuper high frequency (SHF) band extends between 3 GHz and 30 GHz, alsoreferred to as centimeter wave). While the disclosure herein referencesmmWs, it should be understood that the disclosure also applies to nearmmWs. Further, while the disclosure herein refers to mmW base stations,it should be understood that the disclosure also applies to near mmWbase stations. The millimeter wavelength RF channel has extremely highpath loss and a short range.

Aspects described herein (e.g., mmW systems) may be deployed as part ofa 5G NR system. The mmW systems may offer relatively high data rates atrelatively low latencies (e.g., compared to LTE systems). In order tobuild a useful communication network in the millimeter wavelengthspectrum, a beamforming technique may be used, for example, tocompensate for the extreme high path loss. The beamforming techniquefocuses the RF energy into a narrow direction to allow the RF beam topropagate farther in that direction. Using the beamforming technique,non-line of sight (NLOS) RF communication in the millimeter wavelengthspectrum may rely on reflection and/or diffraction of the beams to reachthe UE 404. However, paths and/or clusters between the UE 404 and thebase station 402 may become blocked and new paths and/or clusters maybecome available (e.g., as obstacles, blockers, etc. no longer disrupt apath and/or cluster).

If a path/cluster becomes blocked, either because of movement or changesin the environment (e.g., obstacles, humidity, rain, etc.), a currentserving beam used by the UE 404 may become incoherent (e.g., a radiolink failure may occur, a channel estimate or measurement may fail tosatisfy a threshold, etc.). Thus, in order to provide continuous,seamless coverage for the UE 404, multiple beams in many differentdirections may be used. To that end, the UE 404 may include a pluralityof subarrays 412, 414, 416, 418. Each subarray of the subarrays 412,414, 416, 418 may correspond to the use of a respective plurality ofbeams 420, 422, 424, 426. While the present disclosure illustrates foursubarrays, and each subarray corresponds to the use of four beams, a UEmay include any number of subarrays, and each subarray may correspond tothe use of any number of beams.

One beamforming technique may include codebook-based beam scanning. Acodebook may include a collection of beamforming vectors (e.g., fixedand/or predefined beamforming vectors), as well as techniques forcombining vectors. Blind codebook-based scanning may increase thelatency commensurate with beam switching. With blind codebook-basedscanning, a UE may lack information indicating a preferable beam ordirection and, therefore, the UE may need to measure respective beamqualities for a plurality of beams at a plurality of subarrays in orderto identify and select a preferable beam.

Thus, UEs may benefit from generation of a codebook. For example, the UE404 may include a codebook 410, which may based on a steady-stateapproach, and the UE 404 may dynamically update the codebook whenperforming beam scanning. A codebook may include information indicatingbeamforming vectors (e.g., fixed and/or predefined beamforming vectors),as well as techniques for combining vectors, so that the UE 404 mayprioritize certain beams over others and may refrain from using one ormore beams altogether (e.g., because information in the codebookindicates that such beams are incoherent, blocked, etc.).

In the illustrated aspect, the UE 404 may include a serving subarray412. The UE 404 may communicate with the base station 402 using acurrent serving beam 440, which corresponds to the serving subarray 412.The UE 404 may be configured to use other directional beams of the setof beams 420 of the serving subarray 412. Further, the UE 404 may beconfigured to switch to a new beam of an alternate subarray, forexample, when the new beam is more coherent (e.g., offers higher channelquality) than the current serving beam 440. For example, the UE 404 mayswitch to a new beam of the set of beams 422 corresponding to the firstalternate subarray 414 (e.g., when the UE 404 moves 480 relative to thebase station 402, and the base station 402 becomes base station 402′from the perspective of the UE 404). In various aspects, the UE 404 maybenefit from subarray diversity, as different subarrays may coverdifferent regions, thereby diversifying coherence with respect topaths/clusters.

If the UE 404 is a low-mobility UE, such as a customer-premisesequipment (CPE), beam coherence may not frequently change relatively toa subframe duration. That is, beams may drift in time, but the timescalemay be estimated to be larger or longer than that of a high-mobility UE.

If the UE 404 is a high-mobility UE, beam coherence may change morefrequently relative to the subframe duration. Regardless of UE mobility,arrival and/or blockage of paths/clusters may affect beam coherence. Thearrival/blockage of paths/clusters may be random and, therefore, not apriori predictable, but the UE 404 may be configured to estimate atimescale, either autonomously or with the help of another system (e.g.,the base station 402 and/or a cloud-based server).

The UE 404 may be configured to perform both serving-subarray scanningand alternate-subarray scanning. One or both of these beam scanningprocedures may run in the background at the UE 404 (e.g., the UE 404 maycontinue to communicate using a current serving beam 440 whilecontemporaneously performing the first and/or second type of beamscanning). Moreover, one or both of these scanning procedures may seekneighboring cells provided by neighboring base stations.

The serving-subarray beam scanning may include beam scanning using theset of directional beams 420 corresponding to the serving subarray 412.For example, serving-subarray beam scanning may include beam refinementusing the set of directional beams 420 corresponding to the servingsubarray 412. In an aspect, the UE 404 may perform the serving-subarraybeam scanning based on the codebook 410. For example, the UE 404 mayselect beamforming vectors for directional beams of the serving subarraybased on information indicated in the codebook 410.

The alternate-subarray scanning may include scanning using a respectivepseudo-omni beam 442, 444, 446 of a respective alternate subarray 414,416, 418. A pseudo-omni beam may be a beam with a relatively flat gainin a certain coverage area, which may allow the UE 404 to determine if adirectional beam of alternate subarray is more coherent. However, the UE404 may still perform beam refinement to select a beam of a set ofdirectional beams after determining to switch to an alternate subarray.The UE 404 may attempt to minimize across-module processing (e.g.,beam/subarray pairing) as much as possible. During beam refinementacross an alternate subarray 414, 416, 418, the UE 404 may use thecodebook 410. For example, the UE 404 may select beamforming vectors fordirectional beams of an alternate subarray based on informationindicated in the codebook 410.

In various aspects, the UE 404 may determine whether to perform a firsttype of beam scanning (e.g., serving-subarray scanning) before a secondtype of beam scanning (e.g., alternate-subarray scanning). That is, theUE 404 may prioritize a first type of beam scanning over a second typeof beam scanning. For example, the UE 404 may prioritizeserving-subarray scanning over alternate-subarray scanning, or viceversa.

In one aspect, the UE 404 may determine to perform the first type ofbeam scanning over the second type of beam scanning based on a timescaleassociated with the first type of beam scanning. The timescale maycorrespond to a duration for which a current serving beam is expected orestimated to remain coherent. For example, the timescale may indicate aduration for which the current serving beam 440 is estimated to providesatisfactory communication with the base station 402. When the timescaleis relatively larger, then the UE 404 may prioritize the first type ofbeam scanning (e.g., serving-subarray scanning). However, when thetimescale is relatively smaller, then the UE 404 may prioritize thesecond type of beam scanning (e.g., alternate-subarray scanning). In anaspect, the UE 404 may determine the relative size of the timescale bycomparing the timescale to a threshold—e.g., the UE 404 may determinethat the timescale is relatively large when the timescale meets orexceeds a threshold, but may determine that the timescale is relativelysmall when the timescale does not meet the threshold.

In one aspect, beam coherence may be based on one or more of asignal-to-noise ratio (SNR), a signal-to-interference-plus-noise-ratio(SINR), a signal-to-noise-plus-distortion ratio (SNDR), a receivedsignal strength indicator (RSSI), a reference signal received power(RSRP), a reference signal received quality (RSRQ), a beam referencesignal received power (B-RSRP), or a beam reference signal receivedquality (B-RSRQ). or any combination thereof. For example, the UE 404may measure, using a beam (e.g., the current serving beam 440), at leastone value for an SNR, SINR, SNDR, RSSI, RSRP, RSRQ, B-RSRP, and/orB-RSRQ and compare the at least one measured value to a threshold. Ifthe at least one measured value satisfies the threshold (e.g., meets orexceeds the threshold), then the UE 404 may determine that thecorresponding beam is coherent or satisfactory. Correspondingly, the UE404 may determine that the corresponding beam is incoherent orsatisfactory when the at least one measured value does not satisfy thethreshold (e.g., fails to meet or exceed the threshold).

According to various aspects, the UE 404 may determine the timescalebased on one or more of a mobility of the UE 404, an orientation of theUE 404 relative to a cluster arrival angle and/or a carrier frequency,output data from at least one sensor 408 associated with the UE 404(e.g., an accelerometer, a gyroscope, etc.), and/or one or moremeasurements based on the set of directional beams 420 corresponding tothe serving subarray 412 and/or a respective pseudo-omni beam 442, 444,446 corresponding to a respective alternate subarray 414, 416, 418.

In one aspect, the UE 404 may determine a value for a measurement basedon at least one of an SNR, an SINR, an SNDR, an RSSI, an RSRP, a B-RSRP,and/or a B-RSRQ, and/or any combination thereof. For example, the UE 404may measure a change in coherence (e.g., a change in values measuredover time for one of an SNR, an SINR, an SNDR, an RSSI, an RSRP, aB-RSRP, and/or a B-RSRQ). The UE 404 may calculate the timescale basedon the change in coherence (e.g., the UE 404 may use a relatively largertimescale when the change in coherence is relatively small).

In one aspect, the UE 404 may adjust the timescale based on output fromthe at least one sensor 408. For example, if output from the sensor 408indicates that the UE 404 is frequently moving (e.g., rotating,accelerating, etc.), then the UE 404 may reduce the timescale, e.g.,because the time that the current serving beam 440 is expected to remaincoherent may be reduced.

In one aspect, the UE 404 may determine the timescale based on data 462from the base station 402 and/or data from a cloud-based server (e.g.,similar to the data 462 from the base station 402). For example, the UE404 may receive (e.g., from the base station 402 and/or a cloud-basedserver), a value associated with the timescale, such as a seed valuefrom which the UE 404 may determine the timescale. The UE 404 may usethe seed value in connection with a predetermined algorithm in order tocalculate the timescale.

In another example, the UE 404 may receive (e.g., from the base station402 and/or a cloud-based server) information associated with anenvironment proximate to the UE 404, such as information indicating theavailability of paths/clusters proximate to the UE 404. For example, thebase station 402 may record information associated with paths/clustersof one or more other UEs served by the base station 402, such as one ormore beam switches by another UE, which may indicate the arrival and/ordisappearance of objects that affect paths/clusters. The base station402 may provide this recorded information to the UE 404 as the data 462.Based on the data 462 indicating information associated with theenvironment proximate to the UE 404, the UE 404 may determine (e.g.,calculate) the timescale.

In one aspect, the UE 404 may receive, from the base station 402, asequence of beams 460 from which the UE 404 may determine beamcoherence. The UE 404 may determine the timescale based on the sequenceof beams 460 (e.g., based on tracking the beams of the sequence). Forexample, the UE 404 may receive a sequence of beams from the basestation 402, and the UE 404 may measure one or more values (e.g., RSSIvalue) based on the sequence of beams. Based on the measured one or morevalues, the UE 404 may determine a beam coherence of one or more beams(e.g., change in coherence of the current serving beam 440). When thebeam coherence frequently changes, the UE 404 may determine that asmaller or shorter timescale should be used.

In addition to the determination of the prioritization of beam scanning(e.g., serving-subarray scanning over alternate-subarray scanning, orvice versa), the UE 404 may determine a repetition threshold. Therepetition threshold may indicate a number of repetitions that the UE404 is to perform of the first type of beam scanning before performingthe second type of beam scanning. For example, the UE 404 may be ahigh-mobility UE and, therefore, the orientation of the UE 404 withrespect to the base station 402 may change relatively frequently.Because of this high mobility, the UE 404 may benefit from performingalternate-subarray scanning before serving-subarray scanning, since theprobability that an alternate subarray may offer a better beam than thecurrent serving beam 440 may be greater than the probability that theserving subarray 412 offers a better beam.

In another example, the UE 404 may be a low-mobility UE (e.g., a CPE),which may infrequently change orientation (e.g., a CPE may be at a fixedlocation). Because of this low mobility, the UE 404 may benefit fromperforming serving-subarray scanning before alternate-subarray scanning,since the probability that an alternate subarray may offer a better beamthan the current serving beam 440 may be less than the probability thatthe serving subarray 412 offers a better beam.

In one aspect, the UE 404 may determine the repetition threshold basedon the timescale. For example, the UE 404 may increase the repetitionthreshold as the timescale increases. Correspondingly, the UE 404 maydecrease the repetition threshold as the timescale decreases.Illustratively, the shorter the timescale (e.g., the shorter the amountof time a beam is estimated to remain coherent), the more likely the UE404 may identify a better beam using another type of beam scanning.

The UE 404 may be configured to determine a plurality of timescales. Forexample, the UE 404 may determine a first timescale associated with theserving subarray 412 (e.g., a first timescale that indicates a durationfor which the current serving beam 440 of the set of directional beams420 is estimated to remain coherent before another directional beam ofthe set of directional beams 420 becomes more coherent). Similarly, theUE 404 may determine a second timescale associated with the alternatesubarrays 414, 416, 418 (e.g., a second timescale that indicates aduration for which the set of directional beams 420 includes at leastone coherent beam, and after which the UE 404 may use a beam from analternate subarray 414, 416, 418 that may offer better coherence).

The UE 404 may determine the repetition threshold based on comparison ofthe first and second timescales. For example, if the first timescale andthe second timescale are relatively close, then fewer repetitions of thefirst type of beam scanning may be beneficial before performing thesecond type of beam scanning (e.g., the repetition threshold could beone, if the timescales are approximately the same). Alternatively, ifthe first timescale and the second timescale are appreciably different,then the UE 404 may benefit from performing several repetitions of thefirst type of beam scanning before performing the second type of beamscanning.

In order to find a better beam, the UE 404 may perform the first type ofbeam scanning. The UE 404 may perform the first type of beam scanningbased on codebook 410. The UE 404 may dynamically update the codebook410 as the UE 404 performs the first type of beam scanning (e.g., the UE404 may update information associated with one or more beams, such asbeamforming vectors, as the UE 404 scans through the one or more beams).If the UE 404 is able to find a better beam (e.g., a beam that offersbetter coherence than the current serving beam 440) when performing thefirst type of beam scanning, the UE 404 may switch to the new beam,which becomes the current serving beam.

The UE 404 may repeatedly perform the first type of beam scanning untilthe repetition threshold is reached. That is, the UE 404 may determinewhether a number of unsuccessful repetitions associated with performanceof the first type of beam scanning exceeds the repetition threshold(e.g., an unsuccessful repetition of the first type of beam scanning mayinclude performing the first type of beam scanning without finding abeam that offers better coherence than the current serving beam). If theUE 404 is unable to find a better beam based on performing the firsttype of beam scanning, the UE 404 may then perform the second type ofbeam scanning. That is, the UE 404 may perform the second type of beamscanning based on the determination that the number of unsuccessfulrepetitions meets or exceeds the repetition threshold.

For example, the UE 404 may perform serving-subarray scanning until therepetition threshold is reached (e.g., four repetitions ofserving-subarray scanning) and, if the UE 404 is unable to find a betterbeam using the serving subarray 412, then the UE 404 may performalternate-subarray scanning in order to determine if the UE 404 may usea better beam that corresponds to one of the alternate subarrays 414,416, 418. The UE 404 may perform the second type of beam scanning basedon the codebook 410 and, further, may dynamically update the codebook410 as the UE 404 performs the second type of beam scanning.

In order to determine whether the UE 404 should switch from the currentserving beam 440 to a new serving beam and/or update the codebook 410,the UE 404 may measure one or more values (e.g., an SNR, an SINR, anSNDR, an RSSI, an RSRP, a B-RSRP, and/or a B-RSRQ) based on the firsttype of beam scanning or the second type of beam scanning. In an aspect,the UE 404 may measure a first value based on performance of the firsttype of beam scanning. The first value may be associated with a newserving beam (e.g., another beam of the set of directional beams 420,the new beam 448, etc.). The UE 404 may compare the first value to asecond value that is associated with the current serving beam 440.According to various aspects, the first value and the second value maybe based on an SNR, an SINR, an SNDR, an RSSI, an RSRP, a B-RSRP, and/ora B-RSRQ, or any combination thereof.

If the UE 404 determines that a new serving beam is more coherent thanthe current serving beam 440, then the UE 404 may switch to the newserving beam. In one aspect, the UE 404 may determine that the newserving beam is more coherent than the current serving beam 440 based oncomparison of the first value to the second value.

By way of example, the UE 404 may communicate with the base station 402using the current serving beam 440. The UE 404 may determine one or moretimescales and, based on the time scales, may determine thatalternate-subarray scanning is to be prioritized over serving-subarrayscanning. Further, the UE 404 may determine (e.g., based on thedetermined one or more timescales) that alternate-subarray scanningshould be repeated twice before performing serving-subarray scanning(e.g., the UE 404 may determine the repetition threshold to be two).

Further to this example, the UE 404 may move 480 relative to the basestation 402, so that the UE 404 is orientated toward the base station402′. The UE 404 may perform a first repetition of thealternate-subarray scanning (e.g., while the UE 404 is moving 480), butmay be unsuccessful in determining that a pseudo-omni beam 442, 444, 446indicates an alternate subarray 414, 416, 418 offers a better beam.

Therefore, the UE 404 may perform a second repetition of thealternate-subarray scanning (e.g., after the move 480, so that the UE404 is orientated toward the base station 402′). During this secondrepetition of alternate-subarray scanning, the UE 404 may determine thata first pseudo-omni beam 442 associated with a first alternate subarray414 indicates that the first alternate subarray 414 may offer a beamwith better coherence (e.g., the UE 404 may detect that the energyassociated with the first pseudo-omni beam is above a threshold).Therefore, the UE 404 may perform beam refinement using the set ofdirectional beams 422 corresponding to the first alternate subarray 414.Based on the beam refinement, the UE 404 may switch to a new servingbeam 448 in order to communicate with the base station 402′.

If the UE 404 is unable to determine to switch to a new serving beamafter repeatedly performing the alternate-subarray scanning until therepetition threshold is reached, then the UE 404 may performserving-subarray scanning. With serving-subarray scanning, the UE 404may perform beam refinement using the set of beams 420 corresponding tothe serving subarray.

FIG. 5 illustrates a flowchart of a method of wireless communication.The method may be performed by a UE (e.g., the UE 404, the apparatus802/802′). FIG. 5 may illustrate an approach in which serving-subarrayscanning is prioritized over alternate-subarray scanning.

At operation 502, the UE may use one or more serving beams, including atleast a current serving beam. For example, the UE may send (and encode)and/or receive (and decode) signals through one or more beams. In thecontext of FIG. 4, the UE 404 may use the current serving beam 440, forexample, to communicate with the base station 402.

At operation 504, the UE may perform directional beam refinement, forexample, using beams at a serving subarray of the UE. For example, theUE may measure a respective value associated with a respective beam(e.g., an SNR, an SINR, an SNDR, an RSSI, an RSRP, a B-RSRP, and/or aB-RSRQ) and the UE may select a beam having a best or highestcorresponding measured value. In the context of FIG. 4, the UE 404 mayperform directional beam refinement using the set of beams 420corresponding to the serving subarray 412.

At operation 506, the UE may determine whether another directional beamcorresponding to the serving subarray is better than the serving beam.For example, the UE may compare a first value measured for anotherdirectional beam to a second value measured for the current serving beamand the UE may determine whether the other directional beam offersbetter coherence than the current serving beam—e.g., the UE maydetermine that the other directional beam offers better coherence thanthe current serving beam when the UE determines that the first valueexceeds the second value. In the context of FIG. 4, the UE 404 maydetermine whether another directional beam of the set of directionalbeams 420 is better than the current serving beam 440.

If another directional beam is better than the current serving beam,then the UE may switch to the other directional beam, as illustrated atoperation 510. For example, the UE may adjust a beamforming vector tocorrespond to the other directional beam and the UE may communicatethrough the other directional beam. The UE may then return to operation502 to use the new serving beam. In the context of FIG. 4, the UE 404may switch to another directional beam of the set of directional beams420.

If the UE is unable to determine a better serving beam based ondirectional beam refinement at the serving subarray, the UE maydetermine whether a number of repetitions of beam refinement scanning(i.e., serving-subarray scanning) exceeds a repetition threshold X, asillustrated at operation 508. For example, the UE may determine that noother directional beams of the serving subarray offer better coherencethan the current serving beam after a number of repetitions of theserving-subarray scanning, and the UE may compare the number of timesthe UE has performed the serving-subarray scanning to a repetitionthreshold X. In the context of FIG. 4, the UE 404 may determine whethera number of repetitions of serving-subarray scanning using the servingsubarray 412 exceeds a repetition threshold.

If the number of repetitions does not exceed the repetition threshold X,then the UE may return to operation 504 to perform a next repetition. Inthe context of FIG. 4, the UE 404 may perform another repetition ofserving-subarray scanning.

If the number of repetitions of serving-subarray scanning (e.g., withoutidentifying a beam that offers better coherence) exceeds the repetitionthreshold X, then the UE may proceed to operation 512. At operation 512,the UE may perform pseudo-omni scanning across one or more alternatesubarrays. For example, the UE may select a pseudo-omni beam of analternate subarray and measure a value indicating energy detected forthe selected pseudo-omni beam. In the context of FIG. 4, the UE 404 mayperform alternate-subarray scanning across one or more of the alternatesubarrays 414, 416, 418.

At operation 516, the UE may determine whether the energy associatedwith a pseudo-omni beam corresponding to an alternate subarray exceeds athreshold. For example, the UE may compare the measured value indicatingenergy to a threshold, and the UE may determine whether the measuredvalue indicating energy satisfies the threshold (e.g., meets or exceedsthe threshold). In the context of FIG. 4, the UE 404 may determinewhether the energy associated with a pseudo-omni beam (e.g., the firstpseudo-omni beam 442) exceeds a threshold.

If the UE determines that the energy associated with one or morepseudo-omni beams across one or more alternate subarrays does not exceeda threshold, then the UE may return to operation 502 to continuecommunicating with the current serving beam. In the context of FIG. 4,the UE 404 may determine that the respective energies associated withthe pseudo-omni beams 442, 444, 446 does not exceed a threshold and,therefore, the UE 404 may continue to communicate using the currentserving beam 440.

If the UE determines that the energy associated with one or morepseudo-omni beams across one or more alternate subarrays exceeds athreshold, then the UE may perform beam refinement across the alternatesubarray associated with the pseudo-omni beam having the energyexceeding the threshold (e.g., the alternate subarray associated withthe pseudo-omni beam having a highest value indicating energy), asillustrated at operation 514. For example, the UE may measure arespective value (e.g., an SNR, an SINR, an SNDR, an RSSI, an RSRP, aB-RSRP, and/or a B-RSRQ) for each directional beam of the alternatesubarray, and then select the directional beam of the alternate subarrayhaving the highest or best measured value. In the context of FIG. 4, theUE 404 may perform beam refinement across an alternate subarray (e.g.,the first alternate subarray 414) associated with the pseudo-omni beam(e.g., the first pseudo-omni beam 442) having the energy exceeding thethreshold.

The UE may then determine whether a directional beam corresponding tothe alternate subarray is better than the current serving beam. Forexample, the UE may compare a first value measured for the directionalbeam selected through beam refinement to a second value measured for thecurrent serving beam to determine whether the other directional beamoffers better coherence than the current serving beam. In the context ofFIG. 4, the UE 404 may determine whether the directional beam 448 of theset of directional beams 422 is better than the current serving beam440.

If the other directional beam of the alternate subarray is better thanthe current serving beam, then the UE may switch to the otherdirectional beam, as illustrated at operation 510. For example, the UEmay adjust a beamforming vector to correspond to the other directionalbeam, and the UE may communicate through the other directional beam. TheUE may then return to operation 502 to use the new serving beam. In thecontext of FIG. 4, the UE 404 may switch to the new directional beam 448of the first alternate subarray 414.

FIG. 6 illustrates a flowchart of a method of wireless communication.The method may be performed by a UE (e.g., the UE 404, the apparatus802/802′). FIG. 6 may illustrate an approach in which alternate-subarrayscanning is prioritized over serving-subarray scanning.

At operation 602, the UE may use one or more serving beams, including atleast a current serving beam. For example, the UE may send (and encode)and/or receive (and decode) signals through one or more beams. In thecontext of FIG. 4, the UE 404 may use the current serving beam 440, forexample, to communicate with the base station 402.

At operation 604, the UE may perform alternate-subarray scanning acrossone or more alternate subarrays, for example, in order to determine therespective energies of one or more pseudo-omni beams of one or morealternate subarrays. For example, the UE may select a pseudo-omni beamof an alternate subarray, and the UE may measure a value indicatingenergy detected for the selected pseudo-omni beam of the alternatesubarray. In the context of FIG. 4, the UE 404 may perform steady-statepseudo-omni scanning across one or more alternate subarrays 414, 416,418, for example, in order to determine the respective energies of thepseudo-omni beams 442, 444, 446.

At operation 606, the UE may determine whether the energy associatedwith a pseudo-omni beam corresponding to an alternate subarray exceeds athreshold. For example, the UE may compare a respective value indicatingenergy to a threshold, and the UE may determine whether the measuredvalue indicating energy satisfies the threshold (e.g., meets or exceedsthe threshold). In the context of FIG. 4, the UE 404 may determinewhether the energy associated with a pseudo-omni beam (e.g., the firstpseudo-omni beam 442) exceeds a threshold.

If the UE determines that the energy associated with one or morepseudo-omni beams across one or more alternate subarrays exceeds athreshold, then the UE may perform beam refinement across the alternatesubarray associated with the pseudo-omni beam having the energyexceeding the threshold (e.g., the alternate subarray associated withthe pseudo-omni beam having a highest measured value indicating energy),as illustrated at operation 610. For example, the UE may measure arespective value (e.g., an SNR, an SINR, an SNDR, an RSSI, an RSRP, aBRSRP, and/or a BRSRQ) for each directional beam of the alternatesubarray, and then select the directional beam of the alternate subarrayhaving the highest or best measured value. In the context of FIG. 4, theUE 404 may perform beam refinement across an alternate subarray (e.g.,the first alternate subarray 414) associated with the pseudo-omni beam(e.g., the first pseudo-omni beam 442) having the energy exceeding thethreshold.

The UE may then determine whether a directional beam corresponding tothe alternate subarray is better than the current serving beam, asillustrated at operation 614. For example, the UE may compare a firstvalue measured for the directional beam selected through beam refinementto a second value measured for the current serving beam to determinewhether the other directional beam offers better coherence than thecurrent serving beam. In the context of FIG. 4, the UE 404 may determinewhether the directional beam 448 of the set of directional beams 422 isbetter than the current serving beam 440.

If the other directional beam is better than the current serving beam,then the UE may switch to the other directional beam, as illustrated atoperation 616. The UE may then return to operation 602 to use the newserving beam. In the context of FIG. 4, the UE 404 may switch to the newdirectional beam 448 of the first alternate subarray 414.

If the UE determines that the energy associated with one or morepseudo-omni beams across one or more alternate subarrays does not exceeda threshold, then the UE may determine whether a number of repetitionsof alternate-subarray scanning exceeds a repetition threshold X, asillustrated at operation 608. For example, the UE may determine that noother directional beam of an alternate subarray offers better coherencethan the current serving beam after a number of repetitions of thealternate-subarray scanning, and the UE may compare the number of timesthe UE has performed the alternate-subarray scanning to a repetitionthreshold X. In the context of FIG. 4, the UE 404 may determine whethera number of repetitions of alternate-subarray scanning exceeds arepetition threshold.

If the number of repetitions does not exceed the repetition threshold X,then the UE may return to operation 604 to perform a next repetition ofthe alternate-subarray scanning. In the context of FIG. 4, the UE 404may perform another repetition of alternate-subarray scanning.

If the number of repetitions exceeds the repetition threshold X, thenthe UE may proceed to operation 612. At operation 612, the UE mayperform beam refinement across the serving subarray (i.e.,serving-subarray scanning). For example, the UE may measure a respectivevalue (e.g., an SNR, an SINR, an SNDR, an RSSI, an RSRP, a BRSRP, and/ora BRSRQ) for each directional beam of the serving subarray, and thenselect the directional beam of the serving subarray having the highestor best measured value. In the context of FIG. 4, the UE 404 may performserving-subarray scanning across the serving subarray 412.

At operation 614, the UE may determine whether another directional beamcorresponding to the serving subarray is better than the serving beam.For example, the UE may compare a first value measured for anotherdirectional beam to a second value measured for the current serving beamto determine whether the other directional beam offers better coherencethan the current serving beam. In the context of FIG. 4, the UE 404 maydetermine whether another directional beam of the set of directionalbeams 420 is better than the current serving beam 440.

If another directional beam is better than the current serving beam,then the UE may switch to the other directional beam, as illustrated atoperation 616. The UE may then return to operation 602 to use the newserving beam. In the context of FIG. 4, the UE 404 may switch to anotherdirectional beam of the set of directional beams 420.

If the UE is unable to determine a better serving beam based ondirectional beam refinement at the serving subarray, the UE may returnto operation 602 to continue communicating with the current servingbeam. In the context of FIG. 4, the UE 404 may continue to communicateusing the current serving beam 440.

FIG. 7 is a flowchart of a method 700 of wireless communication. Themethod may be performed by a UE (e.g., the first UE 404, the apparatus902/902′). At 702, the UE may determine to perform a first type of beamscanning before a second type of beam scanning. For example, the UE maydetermine one or more timescales (e.g., a first timescale associatedwith the first type of beam scanning and a second timescale associatedwith a second type of beam scanning), and prioritize the different typesof beam scanning based on the one or more timescales. For example, theUE may determine a first timescale associated with serving-subarrayscanning and a second timescale associated with alternate subarrayscanning, and the UE may prioritize serving-subarray scanning overalternates-subarray scanning, e.g., when the first timescale is shorteror smaller than the second timescale, or vice versa in other aspects. Inthe context of FIG. 4, the UE 404 may determine whether to first performserving-subarray scanning or alternate-subarray scanning.

At operation 704, the UE may perform the first type of beam scanning.For example, the UE may perform serving-subarray scanning oralternate-subarray scanning. In an aspect, the UE may perform the firsttype of beam scanning based on a codebook. For example, the UE mayselect beamforming vectors for directional beams of a serving subarrayor an alternate subarray based on information indicated in the codebook.In the context of FIG. 4, the UE 404 may perform serving-subarrayscanning or alternate-subarray scanning.

For serving-subarray scanning, the UE may measure a respective value(e.g., an SNR, an SINR, an SNDR, an RSSI, an RSRP, a B-RSRP, and/or aB-RSRQ) for each directional beam of the serving subarray, and thendetermine the directional beam of the serving subarray having thehighest or best measured value. The UE may then compare the highest orbest measured value to a value measured for the current serving beam(e.g., (e.g., an SNR, an SINR, an SNDR, an RSSI, an RSRP, a B-RSRP,and/or a B-RSRQ). If the directional beam of the serving subarray hasbetter coherence (e.g., a higher or better measured value) than thecurrent serving beam, then the UE may switch to the directional beam.When the UE switches directional beams, the scanning may be consideredsuccessful. When the UE does not switch directional beams, the scanningmay be considered unsuccessful.

For alternate-subarray scanning, the UE may measure respective valuesindicating energy for respective pseudo-omni beams of alternatesubarrays. When the UE measures a value indicating energy associatedwith a first pseudo-omni beam that exceeds a threshold and is higher orbetter than the other measured values indicating energy associated withother pseudo-omni beams, then the UE may perform beam refinement acrossthe alternate subarray corresponding to the first pseudo-omni beam. TheUE may measure a respective value (e.g., an SNR, an SINR, an SNDR, anRSSI, an RSRP, a BRSRP, and/or a BRSRQ) for each directional beam of thealternate subarray, and then determine the directional beam of thealternate subarray having the highest or best measured value. The UE maythen compare the highest or best measured value to a value measured forthe current serving beam (e.g., (e.g., an SNR, an SINR, an SNDR, anRSSI, an RSRP, a BRSRP, and/or a BRSRQ). If the directional beam of thealternate subarray has better coherence (e.g., a higher or bettermeasured value) than the current serving beam, then the UE may switch tothe directional beam. When the UE switches directional beams, thescanning may be considered successful. When the UE does not switchdirectional beams, the scanning may be considered unsuccessful.

At operation 706, the UE may dynamically update a codebook based oncurrent information associated with a serving beam. For example, whenthe UE performs either the first type of scanning or the second type ofscanning, the UE may update one or more beamforming vectors in order toreflect the results of the first type or second type of scanning. By wayof example, the UE may add or remove beamforming vectors, e.g., based onwhether a measured value associated with a directional beam satisfies athreshold. In the context of FIG. 4, the UE 404 may dynamically updatethe codebook 410 based on current information associated with thecurrent serving beam 440.

At operation 708, the UE may determine whether a number of repetitionsassociated with performance of the first type of beam scanning exceeds arepetition threshold. For example, the UE may count a number ofunsuccessful repetitions performed for the first type of beam scanning,and the UE may compare the number of unsuccessful repetitions to arepetition threshold X. In the context of FIG. 4, the UE 404 maydetermine whether a number of unsuccessful repetitions associated withperformance of the first type of beam scanning exceeds a repetitionthreshold.

At operation 710, the UE may perform the second type of beam scanningbased on the determination that the number of unsuccessful repetitionsexceeded the repetition threshold. In the context of FIG. 4, the UE 404may perform the second type of beam scanning based on the determinationthat the number of unsuccessful repetitions exceeded the repetitionthreshold.

FIG. 8 is a conceptual data flow diagram 800 illustrating the data flowbetween different means/components in an exemplary apparatus 802. Theapparatus may be a UE. The apparatus 802 may include a transmissioncomponent 810 configured to transmit signals to a base station 850. Theapparatus 802 may include a reception component 804 configured toreceive signals from a base station 850.

The apparatus 802 may include a scanning type selection component 812.The scanning type selection component 812 may be configured toprioritize a first type of beam scanning over a second type of beamscanning. In an aspect, the scanning type selection component 812 may beconfigured to determine at least one timescale, and the scanning typeselection component 812 may prioritize the first type of beam scanningover the second type of beam scanning based on the at least one timescale. In one aspect, the scanning type selection component 812 maygenerate the at least one timescale based on beam scanning informationreceived from the base station 850.

The scanning type selection component 812 may provide an indication ofthe beam scanning priority to a beam scanning component 806. The beamscanning component 806 may be configured to perform the first type ofbeam scanning before the second type of beam scanning.

In an aspect, the beam scanning component 806 may be configured todetermine a repetition threshold (e.g., based on the at least onetimescale). The beam scanning component 806 may be configured to performthe first type of beam scanning. The beam scanning component 806 may beconfigured to determine whether a number of unsuccessful repetitionsassociated with performance of the first type of beam scanning exceeds athreshold. The beam scanning component 806 may be configured to performthe second type of beam scanning based on the determination that thenumber of unsuccessful repetitions exceeded the repetition threshold.

In an aspect, the beam scanning component 806 may be configured tomeasure a first value from the performance of the first type of beamscanning. The first value may be associated with a new serving beam. Thebeam scanning component 806 may provide the first value to a beamselection component 808.

The beam selection component 808 may be configured to switch to a newserving beam based on a comparison of the first value to a second valuethat is associated with a current serving beam. The beam selectioncomponent 808 may provide an indication of a selected beam index to thetransmission component 810 and/or the reception component 804 so thatthe apparatus 802 may communicate with the base station 850 using theselected beam.

In an aspect, the beam selection component 808 may be configured todynamically update a codebook based on current information associatedwith a serving beam.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIGS. 5-7.As such, each block in the aforementioned flowcharts of FIGS. 5-7 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 9 is a diagram 900 illustrating an example of a hardwareimplementation for an apparatus 802′ employing a processing system 914.The processing system 914 may be implemented with a bus architecture,represented generally by the bus 924. The bus 924 may include any numberof interconnecting buses and bridges depending on the specificapplication of the processing system 914 and the overall designconstraints. The bus 924 links together various circuits including oneor more processors and/or hardware components, represented by theprocessor 904, the components 804, 806, 808, 810, 812 and thecomputer-readable medium/memory 906. The bus 924 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 914 may be coupled to a transceiver 910. Thetransceiver 910 is coupled to one or more antennas 920. The transceiver910 provides a means for communicating with various other apparatus overa transmission medium. The transceiver 910 receives a signal from theone or more antennas 920, extracts information from the received signal,and provides the extracted information to the processing system 914,specifically the reception component 804. In addition, the transceiver910 receives information from the processing system 914, specificallythe transmission component 810, and based on the received information,generates a signal to be applied to the one or more antennas 920. Theprocessing system 914 includes a processor 904 coupled to acomputer-readable medium/memory 906. The processor 904 is responsiblefor general processing, including the execution of software stored onthe computer-readable medium/memory 906. The software, when executed bythe processor 904, causes the processing system 914 to perform thevarious functions described supra for any particular apparatus. Thecomputer-readable medium/memory 906 may also be used for storing datathat is manipulated by the processor 904 when executing software. Theprocessing system 914 further includes at least one of the components804, 806, 808, 810, 812. The components may be software componentsrunning in the processor 904, resident/stored in the computer readablemedium/memory 906, one or more hardware components coupled to theprocessor 904, or some combination thereof. The processing system 914may be a component of the UE 350 and may include the memory 360 and/orat least one of the TX processor 368, the RX processor 356, and thecontroller/processor 359.

In one configuration, the apparatus 802/802′ for wireless communicationincludes means for determining whether a number of unsuccessfulrepetitions associated with performance of a first type of beam scanningexceeds a repetition threshold. The apparatus 802/802′ may furtherinclude means for performing a second type of beam scanning based on thedetermination that the number of unsuccessful repetitions exceeded therepetition threshold. In an aspect, the performance of the first type ofbeam scanning and the performance of the second type of beam scanningare based on a codebook. The apparatus 802/802′ may further includemeans for dynamically updating the codebook based on current informationassociated with a serving beam.

In an aspect, the number of unsuccessful repetitions has not exceededthe repetition threshold, and the apparatus 802/802′ further includesmeans for measuring a first value from the performance of the first typeof beam scanning, wherein the first value is associated with a newserving beam. The apparatus 802/802′ may further include means forswitching to the new serving beam based on a comparison of the firstvalue and a second value which is associated with a current servingbeam. In an aspect, the first value and the second value are based on asignal-to-noise ratio (SNR), a signal-to-interference-plus-noise-ratio(SINR), a signal-to-noise-plus-distortion ratio (SNDR), a receivedsignal strength indicator (RSSI), a reference signal received power(RSRP), or a beam reference signal received quality (B-RSRP), or anycombination thereof.

The apparatus 802/802′ may further include means for determining toperform the first type of beam scanning before the second type of beamscanning. In an aspect, the determination to perform the first type ofbeam scanning before the second type of beam scanning is based on atimescale associated with the first type of beam scanning. The apparatus802/802′ may further include means for determining the repetitionthreshold based on the timescale. In an aspect, the timescale isdetermined based on at least one of a mobility of the UE, an orientationof the mobility of the UE relative to a cluster arrival angle and acarrier frequency, output data from at least one sensor associated withthe UE, data from a cloud-based server, or data from a base station. Inan aspect, the data from the base station or the data from thecloud-based server includes at least one of a sequence of beams fromwhich the UE determines beam coherence, information about an environmentproximate to the UE, or a value associated with the timescale. In anaspect, the first type of beam scanning includes beam refinement using afirst set of directional beams associated with a first subarray, thefirst subarray corresponding to use of a current serving beam, andwherein the second type of beam scanning includes beam scanning using apseudo-omni beam associated with a second subarray that is differentfrom the first subarray. In an aspect, the first type of beam scanningincludes beam scanning using a pseudo-omni beam associated with a secondsubarray that is different from a first subarray, the first subarraycorresponding to use of a current serving beam, and wherein the secondtype of beam scanning includes beam refinement using a first set ofdirectional beams associated with the first subarray.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 802 and/or the processing system 914 of theapparatus 802′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 914 mayinclude the TX Processor 368, the RX Processor 356, and thecontroller/processor 359. As such, in one configuration, theaforementioned means may be the TX Processor 368, the RX Processor 356,and the controller/processor 359 configured to perform the functionsrecited by the aforementioned means.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication by a userequipment (UE), the method comprising: determining whether a number ofunsuccessful repetitions associated with performance of a first type ofbeam scanning exceeds a repetition threshold; and performing a secondtype of beam scanning based on the determination that the number ofunsuccessful repetitions exceeded the repetition threshold, wherein thefirst type of beam scanning includes beam scanning using a flat gainbeam or pseudo-omni beam associated with a plurality of subarrays thatare different from a first subarray, the first subarray corresponding touse of a current serving beam, and wherein the second type of beamscanning includes beam refinement using a set of directional beamsassociated with the first subarray.
 2. The method of claim 1, whereinthe performance of the first type of beam scanning and the performanceof the second type of beam scanning are based on a codebook.
 3. Themethod of claim 2, further comprising: dynamically updating the codebookbased on current information associated with a serving beam.
 4. Themethod of claim 1, wherein when the number of unsuccessful repetitionshas not exceeded the repetition threshold, and the method furthercomprising: measuring a first value from the performance of the firsttype of beam scanning, wherein the first value is associated with a newserving beam; and switching to the new serving beam based on acomparison of the first value and a second value which is associatedwith a current serving beam.
 5. The method of claim 4, wherein the firstvalue and the second value are based on a signal-to-noise ratio (SNR), asignal-to-interference-and-noise-ratio (SINR), asignal-to-noise-plus-distortion ratio (SNDR), a received signal strengthindicator (RSSI), a reference signal received power (RSRP), or areference signal received quality (RSRQ), or any combination thereof. 6.The method of claim 1, further comprising: determining to perform thefirst type of beam scanning before the second type of beam scanning. 7.The method of claim 6, wherein the determination to perform the firsttype of beam scanning before the second type of beam scanning is basedon a timescale associated with the first type of beam scanning andchanges in channel conditions as observed by the UE.
 8. The method ofclaim 7, further comprising: determining the repetition threshold basedon the timescale and channel conditions.
 9. The method of claim 7,wherein the timescale is determined based on at least one of a mobilityof the UE, an orientation of the mobility of the UE relative to acluster arrival angle and a carrier frequency, output data from at leastone sensor associated with the UE, blockage or fading conditions asobserved by the UE, data from a cloud-based server, or data from a basestation.
 10. The method of claim 9, wherein the data from the basestation or the data from the cloud-based server includes at least one ofa sequence of beams from which the UE determines beam coherence,information about an environment proximate to the UE, or a valueassociated with the timescale.
 11. A method of wireless communication bya user equipment (UE), the method comprising: determining whether anumber of unsuccessful repetitions associated with performance of afirst type of beam scanning exceeds a repetition threshold; andperforming a second type of beam scanning based on the determinationthat the number of unsuccessful repetitions exceeded the repetitionthreshold, wherein the first type of beam scanning includes beamrefinement using a first set of directional beams associated with afirst subarray, the first subarray corresponding to use of a currentserving beam, and wherein the second type of beam scanning includes beamscanning using a flat gain beam or pseudo-omni beam associated with aplurality of subarrays that are different from the first subarray. 12.The method of claim 11, wherein the performance of the first type ofbeam scanning and the performance of the second type of beam scanningare based on a codebook.
 13. The method of claim 12, further comprising:dynamically updating the codebook based on current informationassociated with a serving beam.
 14. The method of claim 11, wherein whenthe number of unsuccessful repetitions has not exceeded the repetitionthreshold, and the method further comprising: measuring a first valuefrom the performance of the first type of beam scanning, wherein thefirst value is associated with a new serving beam; and switching to thenew serving beam based on a comparison of the first value and a secondvalue which is associated with a current serving beam.
 15. The method ofclaim 14, wherein the first value and the second value are based on asignal-to-noise ratio (SNR), a signal-to-interference-and-noise-ratio(SINR), a signal-to-noise-plus-distortion ratio (SNDR), a receivedsignal strength indicator (RSSI), a reference signal received power(RSRP), or reference signal received quality (RSRQ), or any combinationthereof.
 16. The method of claim 11, further comprising: determining toperform the first type of beam scanning before the second type of beamscanning and changes in channel conditions as observed by the UE. 17.The method of claim 16, wherein the determination to perform the firsttype of beam scanning before the second type of beam scanning is basedon a timescale associated with the first type of beam scanning andchannel conditions.
 18. The method of claim 17, further comprising:determining the repetition threshold based on the timescale.
 19. Themethod of claim 17, wherein the timescale is determined based on atleast one of a mobility of the UE, an orientation of the mobility of theUE relative to a cluster arrival angle and a carrier frequency, outputdata from at least one sensor associated with the UE, blockage or fadingconditions as observed by the UE, data from a cloud-based server, ordata from a base station.
 20. The method of claim 19, wherein the datafrom the base station or the data from the cloud-based server includesat least one of a sequence of beams from which the UE determines beamcoherence, information about an environment proximate to the UE, or avalue associated with the timescale.
 21. An apparatus for wirelesscommunication, comprising: a transceiver; a memory configured to storeinstructions; and one or more processors communicatively coupled withthe transceiver and the memory, wherein the one or more processors areconfigured to: determine whether a number of unsuccessful repetitionsassociated with performance of a first type of beam scanning exceeds arepetition threshold; and perform a second type of beam scanning basedon the determination that the number of unsuccessful repetitionsexceeded the repetition threshold, wherein the first type of beamscanning includes beam scanning using a flat gain beam or pseudo-omnibeam associated with a plurality of subarrays that are different from afirst subarray, the first subarray corresponding to use of a currentserving beam, and wherein the second type of beam scanning includes beamrefinement using a set of directional beams associated with the firstsubarray.
 22. The apparatus of claim 21, wherein the performance of thefirst type of beam scanning and the performance of the second type ofbeam scanning are based on a codebook.
 23. The apparatus of claim 22,wherein the one or more processors is further configured to dynamicallyupdate the codebook based on current information associated with aserving beam.
 24. The apparatus of claim 21, wherein when the number ofunsuccessful repetitions has not exceeded the repetition threshold, andthe one or more processors is further configured to: measure a firstvalue from the performance of the first type of beam scanning, whereinthe first value is associated with a new serving beam; and switch to thenew serving beam based on a comparison of the first value and a secondvalue which is associated with a current serving beam.
 25. The apparatusof claim 24, wherein the first value and the second value are based on asignal-to-noise ratio (SNR), a signal-to-interference-and-noise-ratio(SINR), a signal-to-noise-plus-distortion ratio (SNDR), a receivedsignal strength indicator (RSSI), a reference signal received power(RSRP), or a reference signal received quality (RSRQ), or anycombination thereof.
 26. The apparatus of claim 21, wherein the one ormore processors is further configured to determine to perform the firsttype of beam scanning before the second type of beam scanning.
 27. Theapparatus of claim 26, wherein the determination to perform the firsttype of beam scanning before the second type of beam scanning is basedon a timescale associated with the first type of beam scanning andchanges in channel conditions as observed by the UE.
 28. The apparatusof claim 27, wherein the one or more processors is further configured todetermine the repetition threshold based on the timescale and channelconditions.
 29. The apparatus of claim 27, wherein the timescale isdetermined based on at least one of a mobility of the UE, an orientationof the mobility of the UE relative to a cluster arrival angle and acarrier frequency, output data from at least one sensor associated withthe UE, blockage or fading conditions as observed by the UE, data from acloud-based server, or data from a base station.
 30. The apparatus ofclaim 29, wherein the data from the base station or the data from thecloud-based server includes at least one of a sequence of beams fromwhich the UE determines beam coherence, information about an environmentproximate to the UE, or a value associated with the timescale.
 31. Anapparatus for wireless communication, comprising: a transceiver; amemory configured to store instructions; and one or more processorscommunicatively coupled with the transceiver and the memory, wherein theone or more processors are configured to: determine whether a number ofunsuccessful repetitions associated with performance of a first type ofbeam scanning exceeds a repetition threshold; and perform a second typeof beam scanning based on the determination that the number ofunsuccessful repetitions exceeded the repetition threshold, wherein thefirst type of beam scanning includes beam refinement using a first setof directional beams associated with a first subarray, the firstsubarray corresponding to use of a current serving beam, and wherein thesecond type of beam scanning includes beam scanning using a flat gainbeam or pseudo-omni beam associated with a plurality of subarrays thatare different from the first subarray.
 32. The apparatus of claim 31,wherein the performance of the first type of beam scanning and theperformance of the second type of beam scanning are based on a codebook.33. The apparatus of claim 32, wherein the one or more processors isfurther configured to dynamically update the codebook based on currentinformation associated with a serving beam.
 34. The apparatus of claim31, wherein when the number of unsuccessful repetitions has not exceededthe repetition threshold, and the one or more processors is furtherconfigured to: measure a first value from the performance of the firsttype of beam scanning, wherein the first value is associated with a newserving beam; and switch to the new serving beam based on a comparisonof the first value and a second value which is associated with a currentserving beam.
 35. The apparatus of claim 34, wherein the first value andthe second value are based on a signal-to-noise ratio (SNR), asignal-to-interference-and-noise-ratio (SINR), asignal-to-noise-plus-distortion ratio (SNDR), a received signal strengthindicator (RSSI), a reference signal received power (RSRP), or referencesignal received quality (RSRQ), or any combination thereof.
 36. Theapparatus of claim 31, wherein the one or more processors is furtherconfigured to determine to perform the first type of beam scanningbefore the second type of beam scanning and changes in channelconditions as observed by the UE.
 37. The apparatus of claim 36, whereinthe determination to perform the first type of beam scanning before thesecond type of beam scanning is based on a timescale associated with thefirst type of beam scanning and channel conditions.
 38. The apparatus ofclaim 37, wherein the one or more processors is further configured todetermine the repetition threshold based on the timescale.
 39. Theapparatus of claim 37, wherein the timescale is determined based on atleast one of a mobility of the UE, an orientation of the mobility of theUE relative to a cluster arrival angle and a carrier frequency, outputdata from at least one sensor associated with the UE, blockage or fadingconditions as observed by the UE, data from a cloud-based server, ordata from a base station.
 40. The apparatus of claim 39, wherein thedata from the base station or the data from the cloud-based serverincludes at least one of a sequence of beams from which the UEdetermines beam coherence, information about an environment proximate tothe UE, or a value associated with the timescale.